At the present time, there are a variety of furnaces and heating systems available for heating buildings, particularly houses or single family dwellings.
Commonly, in most developed countries, fossil fuel is used, eg. oil, gas, coal or coke. The latter two fuels have become less common for domestic use, due to handling problems. It is difficult and expensive to provide any sort of automatic handling and feeding arrangement for such solid fuels. Oil and gas on the other hand have the advantage that, being fluids, it is a relatively simple matter to regulate their flow to a furnace or water heater. As a consequence, furnaces and water heaters and other heating appliances fueled by oil and gas can be run automatically and left unattended for long periods. Oil and gas can both be stored in relatively large quantities and a combustion chamber configuration for automatic operation can readily be designed.
At the present time, the use of wood as a fuel is regaining popularity in various parts of North America and elsewhere. In many developing countries, and underdeveloped countries, wood is a significant energy source. In appropriate areas, it has the advantage that it is readily available and relatively inexpensive. Typically, in a house or single unit dwelling, the wood is burnt in a fireplace, which may be open or closed, or in a freestanding wood stove or in a furnace or boiler. Water heating units can be incorporated, as desired. Wood, however, like coal and coke, suffers from the disadvantage of being a solid fuel. This makes it necessary to manually fuel a heating unit at regular intervals. Also, wood has a relatively low heat value per unit volume, necessitating relatively frequent fueling of the stove or furnace.
One difficulty with a wood burning appliance is to operate it efficiently for a long period of time. For a conventional wood burning appliance, if it is operated efficiently, it will consume a charge of wood in a relatively short time and give excessive power output. The combustion time can be extended, by reducing the combustion rate, e.g. by restricting the air supply. However, this results in inefficient combustion. This in turn can result in uncombusted material being deposited in the flue, which can cause a fire, or being vented to the atmosphere as pollutants.
One solution to this problem is to provided a fuel store which is separate from the combustion chamber, but is still an integral part of the whole appliance. As discussed below, there are numerous earlier patents suggesting such a possibility. Some door designs provide a movable baffle suspended across the top of the door, which is displaced by solid fuel passing through. The difficulty with a fuel store is to both ensure that feeding of fuel to the combustion is simple and reliable, and also that the fuel store can be simply and easily recharged.
The fuel store can be provided to one side of the combustion chamber, and this diminishes the likelihood of the escape of noxious gases, while also reducing the possibility of combustion extending into the fuel store.
For simplicity of feeding fuel to the combustion chamber, the fuel store should be provided directly above the combustion chamber. However, one then has the problem of preventing combustion from extending into the fuel store and also the problem of preventing the escape of hot, noxious fumes to the exterior.
Most contemporary doors are quite simple, and when opened to admit fuel into the fuel store, give a direct passage between the exterior and the fuel store. For many configurations, in operation, the fuel store is full of hot, noxious gases under pressure. Consequently, when the door is opened, these gases, smoke etc. are vented to atmosphere. The problem can be reduced by placing a door lower down, but ideally one needs to charge a fuel store from the top.
It is to be appreciated that, as well as separate fuel stores, this difficulty with a door mechanism is present in conventional solid fuel appliances. Thus, most conventional door designs do not tackle the problem of preventing or reducing the escape of smoke and hot noxious fumes when the door is open to recharge the furnace.
The prior art teaches a number of door mechanisms for feeding fuel into a magazine of a solid fuel appliance. By way of example, U.S. Pat. No. 794,853 (Cox) shows an inclined fuel chute with a series of division doors in it, which can be operated independently, to supply batches of fuel. However, these doors are not intended to provide a lock effect for feeding of a fresh supply at regular intervals.
U.S. Pat. No. 1,152,363 (Weisberger), like many other patents, discloses just a single door for feeding fuel.
U.S. Pat. No. 2,394,811 (Rymer), discloses a door mechanism intended to eliminate substantially the escape of smoke and fumes from a combustion chamber. A stove is provided with an outer door and an inner closure member. The closure member is pivoted in the upper part of the combustion chamber. Each of the side walls of the closure member is provided with a pivoted dog and the outer door is provided with lugs on either side. In the closed position, the lugs are positioned below the dogs. During an opening movement of the door, the dogs are free to swing in a counterclockwise direction about their pivot axes, thereby permitting free opening movement of the door without any corresponding movement of the closure member. When the door arrives at its open position, the lugs have moved to such an extent that they then engage the dogs. The space between the door and the closure member is charged with fuel. When the door is closed, the lugs push on the dogs and open the closure member. This enables the fuel to drop down into the interior of the stove. When the door reaches its fully closed position, the lugs disengage the dogs, permitting the closure member to return to the closed position, ready for the next charging of the stove. A disadvantage with the Rymer arrangement is that there is no positive displacement of the fuel from the space between the closure member and the door. Clearly, any fuel left here will become hot. Consequently, if the door is then opened, fumes and the like will be released. There may also be a fire hazard.
U.S. Pat. No. 4,126,119 (Fike) is an example of a disclosure of a heating device, in which a fuel supply is provided. Here, the mechanism for feeding logs is simply a door at the outer end of the device.
A somewhat complex feeding arrangement is disclosed in U.S. Pat. No. 4,185,567 (Grossnicklaus). This is of some interest in showing the complexity that can arise when a feed other than gravitational is employed. Here, Grossniklaus relies upon the arrangement of a ram and the fuel store beside the combustion chamber to keep the combustion gases out of the fuel store. Three separate flaps are provided for displacing the wood towards a ram, and the ram drives the wood through a feed duct into the combustion chamber.
U.S. Pat. No. 4,339,998 (Finch) relies upon gravity feed the end of a conveyor, and a counterweighted self-closing door is provided.
Similarly, U.S. Pat. No. 4,442,825 (Waldau) provides a feeding device which relies upon a gravity feed. It has doors at either end, but again no positive displacement of the fuel is provided.
An automatic log feeder is provided in U.S. Pat. No. 4,444,538 (Manley), but this again relies upon a simple gravity feed and a flap-type door at the entry to the fireplace.
U.S. Pat. No. 4,530,289 (Godbout) discloses a solid fuel furnace, in which a feeder is closed to the atmosphere, to prevent combustion extending into it. However, it does not include any mechanism enabling it to be charged in use, whilst preventing fumes escaping. U.S. Pat. No. 4,606,282 (Steindal) is similar in this respect. It provides for feeding of fuel to a combustion zone, while preventing the flow of air through the wood storage area. However, it again does not provide any interlock door mechanism to prevent the escape of fumes if it is charged in use.